If we were having the discussion face to face rather than through the to-and-fro of this forum, you would probably find my body language and facial expressions more illuminating than these typed words - a "I'm sure something doesn't fit here but I can't articulate it properly" kind of look.

By comparing crash speed with free-travelling speed we are acknowledging that 'something' happened in between (obviously). I'll call it the 'gap' from here on if that's OK. That 'something' includes road user response but is also a function of:

AbilityVehicle factorsEnvironmental factorsHow the individual was driving before responding.

Indentical circumstances could lead to differening outcomes if response is different, ergo differing circumstances and reactions could lead to the same outcomes. Thus, I feel that is wrong to call the gap 'user response' because, unless we can quantify all of the other extraneous factors we are unaware of just how effective user response was.Thus, the gap is not 'user response' per-se, but exists as a result of user response and its effectiveness is dependent upon the pot-pourri of other factors one of which is the free travelling speed prior to response.Therefore if the effectiveness of user response is dependent upon, amongst other things, free travelling speed - how can we elevate this intangible above the tangible in degree of importance?

Owww my head hurts

I'm sorry your head hurts. Take any time you need if you want to reply again.

Those factors you list are all within road user response (at least according to the nice broad definition in my head).

The last one is one of the most important. All speeds ae chosen. Where a reduced speed exists in an area of danger, that too is a "road user response" to the visible danger in the location. On this basis, the "gap" is always between free travelling speed and impact speed.

One important part of the road safety system that's frequently missed is the iterative and closed loop nature of individual speed control.

OK, I took all weekend to think this through and re-read the 12 mph page again a couple of times.

SafeSpeed wrote:

Those factors you list are all within road user response (at least according to the nice broad definition in my head).

Hmmm, a question of semantics then. Obviously I was thinking only of how the road user(s) reacted not all of the other factors as well. By so doing I believe you are stretching the definition of the word 'response' to breaking point.

Looking at the original assertion (that resonse is more important than free travelling speed in determining crash outcome) it still looks to me that you have 'discovered' the obvious. If only a small proportion of incidents involving collisions occurs at a speed that results in deaths, and that the number of smaller incidents is of several orders of magnitude higher, then it stands to reason that the average collision speed will work out on the low side. It simply demonstrates that there are loads of little crashes and much fewer big ones in any given period of time.
Reducing the speed of vehicles by a few miles per hour may not affect the average crash speed (i.e. that across the whole system) by a lot, but if applied to a particular stretch of road (and enforced by a camera), it may well do at that particular site alone.

OK, I took all weekend to think this through and re-read the 12 mph page again a couple of times.

SafeSpeed wrote:

Those factors you list are all within road user response (at least according to the nice broad definition in my head).

Hmmm, a question of semantics then. Obviously I was thinking only of how the road user(s) reacted not all of the other factors as well. By so doing I believe you are stretching the definition of the word 'response' to breaking point.

If I'm "stretching the definition to breaking point" then that means I used the wrong term in the first place. As it happens, I'm pretty comfortable with the term, but your view of it might help explain why quite a few folk have had problems with the page.

Can you suggest a short phrase that would meet my nice broad definition?

Rigpig wrote:

Looking at the original assertion (that resonse is more important than free travelling speed in determining crash outcome) it still looks to me that you have 'discovered' the obvious. If only a small proportion of incidents involving collisions occurs at a speed that results in deaths, and that the number of smaller incidents is of several orders of magnitude higher, then it stands to reason that the average collision speed will work out on the low side. It simply demonstrates that there are loads of little crashes and much fewer big ones in any given period of time.Reducing the speed of vehicles by a few miles per hour may not affect the average crash speed (i.e. that across the whole system) by a lot, but if applied to a particular stretch of road (and enforced by a camera), it may well do at that particular site alone.

With the ultimate contribution of "road user reponse" (my definition!) being far greater than free travelling speed (in terms of mitigated crash severity), my next assertion is that the means of speed enforcement is likely to diminish response to a greater degree than the potential benefit of a reduced free travelling speed.

I don't expect to see a reduction in crashes (caused by the camera) even at speed camera sites. Rather the opposite, and no data yet published suggests that I am in error.

If I'm "stretching the definition to breaking point" then that means I used the wrong term in the first place. As it happens, I'm pretty comfortable with the term, but your view of it might help explain why quite a few folk have had problems with the page.

Can you suggest a short phrase that would meet my nice broad definition?

Hmm, what about The Response Effect? I'll try to think of something better that encapsulates the whole package.

But I maintain that that this 'contribution' is an illusion created by the fact that, across the entire system, there are more low severity crashes than high severity ones. Any further assertions based on this point become meaningless, in my mind at least.
Sorry Paul but I'm no nearer being convinced that you're on to something with this 'user respones' thing.

But I maintain that that this 'contribution' is an illusion created by the fact that, across the entire system, there are more low severity crashes than high severity ones. Any further assertions based on this point become meaningless, in my mind at least.

It's not just MORE low severity crashes is it? It's oodles more at the very least. Why does the system favour low severity outcomes so hugely? Answer: Because crash severity is largely a function of degree of driver error. Have you seen this page:

This pattern is present across all accident types. In health and safety literature (regarding industrial accidents) they call the pattern "the risk triangle". In Health and safety they work to reduce the number of incidents in the knowledge that this will also affect the number of high severity outcomes.

Rigpig wrote:

Sorry Paul but I'm no nearer being convinced that you're on to something with this 'user respones' thing.

Sure. I understand. Keep looking around, and feel free to ask any questions. You might find a flaw in my logic, and if you do I want to hear about it!

This pattern is present across all accident types. In health and safety literature (regarding industrial accidents) they call the pattern "the risk triangle". In Health and safety they work to reduce the number of incidents in the knowledge that this will also affect the number of high severity outcomes.

Yeah I know, used to teach this But of course if we reduce overall vehicle speeds, we may not affect the oodles of small shunts and incidents by a lot, but we may bite into the more severe incidents where driver reaction would have been more effective had they been going slower....

Look, let me present a logical fallacy of my own....

I have a bucket containing 1,000 ball bearings: 980 small ones and 20 big ones. Of the small ones:

500 are Yellow
120 are Red
120 are Green
120 are Blue
120 are Orange

I also have four of each of the above colours in the large size. I work out that if I pick out a ball at random I have a:

2:1 chance of it being small and yellow
8.3:1 chance of it being small and red
8.3:1 chance of it being small and green
8.3:1 chance of it being small and blue
8.3:1 chance of it being small and orange

I therefore conclude that the chances of pulling out a small ball at random are dependant upon it being yellow

This pattern is present across all accident types. In health and safety literature (regarding industrial accidents) they call the pattern "the risk triangle". In Health and safety they work to reduce the number of incidents in the knowledge that this will also affect the number of high severity outcomes.

Yeah I know, used to teach this But of course if we reduce overall vehicle speeds, we may not affect the oodles of small shunts and incidents by a lot, but we may bite into the more severe incidents where driver reaction would have been more effective had they been going slower....

I certainly don't rule out the possibility of a strategy that might affect medium to high severity outcomes. Seat belts might be one - they won't improve damage only accidents but might save lives or serious injuries.

But here in this discussion (and in the references we're discussing) I'm trying to illuminate the fundamentals.

Rigpig wrote:

Look, let me present a logical fallacy of my own....

I have a bucket containing 1,000 ball bearings: 980 small ones and 20 big ones. Of the small ones:

500 are Yellow120 are Red120 are Green120 are Blue120 are Orange

I also have four of each of the above colours in the large size. I work out that if I pick out a ball at random I have a:

2:1 chance of it being small and yellow8.3:1 chance of it being small and red8.3:1 chance of it being small and green8.3:1 chance of it being small and blue8.3:1 chance of it being small and orange

I therefore conclude that the chances of pulling out a small ball at random are dependant upon it being yellow

This is what I see when I look at your argument.

I'm really trying hard to understand your point. Are you trying to illustrate the difference between coincidence and causation? If you are, I don't see how it is relevant. I don't think I'm making any assumptions about causation or coincidence.

I'm really trying hard to understand your point. Are you trying to illustrate the difference between coincidence and causation? If you are, I don't see how it is relevant. I don't think I'm making any assumptions about causation or coincidence.

Neither, in fact I'll admit I didn't make the point very well. What I should have concluded was that the chances of pulling out a small ball were directly related to it's size - which is of course true because it's blindingly obvious. All of the other information is irrelevant.

Relating this to your assertion, the same holds true. Crash severity is mitigated by driver response so the numbers are always going to be crunched in favour of this argument, the magnitude of favour depends on how many of the oodles of little accidents we choose to include (particularly if we count ones where the chances of being killed are very small indeed). This is unless we go off into the land of the fanciful....
For free travelling speed to be considered more important, using your calculations, a driver would have to accelerate into the crash having spotted a hazard.
Ergo, for the two to equally significant, the driver would not respond at all giving us an oxymoron.
It is like saying that to win a football match scoring goals is more important than conceding them. If it were equally as important then you'd get a draw, less important and you'd lose. And the significance of scoring goals increases the more you concede...its obvious.
I'll conclude by asking this. Do any independent road safety specialists see the 12mph argument as having anything significant to contribute towards road safety in the UK?

What I should have concluded was that the chances of pulling out a small ball were directly related to it's size - which is of course true because it's blindingly obvious. All of the other information is irrelevant.

I still don't get it. I've even taken a couple of days to see if it sank in. However, this next bit looks more understandable.

Rigpig wrote:

Relating this to your assertion, the same holds true. Crash severity is mitigated by driver response so the numbers are always going to be crunched in favour of this argument, the magnitude of favour depends on how many of the oodles of little accidents we choose to include (particularly if we count ones where the chances of being killed are very small indeed). This is unless we go off into the land of the fanciful....

I don't actually see any reason why this is true. Suppose we just looked at accidents on high speed roads. We know that a crash delta v of 70 mph is very likely to result in a death. If we were all crashing at full speed, we'd all be dead - we wouldn't have to have "oodles of little accidents" at all.

The fact that we do have oodles of little accidents is the critical observation that leads us to the question: "why do we have oodles of little accidents?"

Rigpig wrote:

For free travelling speed to be considered more important, using your calculations, a driver would have to accelerate into the crash having spotted a hazard.Ergo, for the two to equally significant, the driver would not respond at all giving us an oxymoron.

That's not right for the reasons given above.

Rigpig wrote:

It is like saying that to win a football match scoring goals is more important than conceding them. If it were equally as important then you'd get a draw, less important and you'd lose. And the significance of scoring goals increases the more you concede...its obvious.I'll conclude by asking this. Do any independent road safety specialists see the 12mph argument as having anything significant to contribute towards road safety in the UK?

I don't know the answer to your last question off hand. I have had a number of private email comments on the page, many of which have been supportive. I have "always" had a policy of posting criticisms and I can tell you for sure that no one has found anything that I believe to be a material error.

1. Driver travelling NSL road at 60mph. They round a corner and are confronted by a farm vehicle across the road. Little time to react, the driver crashes into the farm vehicle. Delta V is 45mph and the driver sadly dies.

2. Driver travelling along an urban street at 30mph notices some kids playing up ahead. He eases off the accelerator just before his suspicions are confirmed - one of the kids cycles off the pavement into the road. The driver has sufficient time to brake safely to a halt and misses the startled kid. Delta V 0mph

3. The other 8 incidents happen in urban settings as well. They are the little shunts and knocks that occur at roundabouts, in carparks, in queues of traffic etc. The Delta V in each case is 5mph (because they were travelling slowly in the first instance). Nobody dies, a few escape injury and there are some cases of whiplash.

No it didn't, it saved one life. In eight of the incidents the speeds were so low that nobody would have died even if none of the drivers reacted in any way.

And the one life that was saved was as a result of the natural and expected behaviour of a sentient human - hardly a great revelation. Thus, my point is that you are making an extravagant claim for the benefit of a phenomenon whose characteristics cannot be realistically ascertained without conducting a number of 'no reaction' experiments at varying speeds.

We really must get away from this fixation that x mph is intrinsically safe, and look at the real causes of accidents.

That isn't the point I'm attempting to make. There may well be a number of low speed incidents in which soemone dies, but there are oodles in which nobody dies, nor would have died even if the driver concerened did nothing to avoid it.

WHY EXACTLY were the drivers going slow enough to have minors in the first place?

NOT doing 70mph in town is also a very valuable driver behaviour. Try thinking about how and why you don't drive through a narrow village high street (one of the few that's still NSL) at 60mph. Your answer will also be a component of my "driver response".

WHY EXACTLY were the drivers going slow enough to have minors in the first place?

Because they were in carparks and in queues of traffic where, unless you are driving a chieftain tank, you are forced to go at the speed of queue i.e. edging along at 5-10mph in the first place. Yet people still get hurt in these little shunts and these 'accidents' will be included in the oodles of minor injuries data.
A work colleague was shunted up the backside by someone at a roundabout (thought he was going to pull out but he didn't - classic incident). He was off work for three weeks with whplash and is now seeking compensation.
Other driver's reaction = NONE, she just drove into him.
Speed? (5-10 mph max)

Because they were in carparks and in queues of traffic where, unless you are driving a chieftain tank, you are forced to go at the speed of queue i.e. edging along at 5-10mph in the first place. Yet people still get hurt in these little shunts and these 'accidents' will be included in the oodles of minor injuries data.

I appreciate that where you drive daily the opportuinities to drive recklessly fast may be infrequent.

Where I drive daily (North Scotland) traffic does not usually constrain, yet reckless speeds are extremely rare.

I don't doubt that the constraints of traffic play a part - a valid point that you have correctly highlighted - but it is more generally true that restraint rather than constraint makes the difference.

But there's another dimension that I need to bring in at this point. Suppose we have a hypothetical maniac driver. He might turn out to be rather safe when fully constrained in traffic. Yet, the moment he is unconstrained he rushes off at reckless speed and has his crash. In this way the risks that you fear are very strongly biased towards the commonplace unconstrained situations.

Should have had his head restraint properly adjusted to manufacturer's recommendations, then.

<Irritated mode = ON>
Perhaps he did
Perhaps he was craning his neck watching the traffic
Perhaps his car didn't have one
Or perhaps the minute of what happened in this one little incident is utterly irrelevant within the context of the wider discussion going on above (you did read it all before posting didn't you?). What is important is that he was hurt in a small sub 30mph shunt, one of many similar incidents which happen each and every day. One in which there was no mitigating driver response.
<Irritated mode =OFF>

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